From a spec perspective there's no limitation that all components in a module or application have to be one or the other. Each stateless session bean can be implemented as either a JAX-WS or JAX-RPC endpoint. Of course, JAX-WS is the recommended approach going forward. JAX-RPC will be a candidate for pruning from a future version of the Java EE platform and will not be available as an option for the new EJB 3.1 Singleton component.
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